This invention relates to power detectors as employed in electrical circuits in general. The invention also relates to power detectors associated with high power amplifiers and, in particular, but not exclusively, relates to power detectors associated with telecommunications high power and high frequency power amplifiers. The invention also relates to switching amplifier/attenuator blocks.
It is a problem in the field of electrical circuits and amplifiers in general, and, in particular, transmit power amplifiers to precisely and dynamically control the operation of the amplifying elements that comprise the amplifier. In the case of cellular radio transmit amplifiers, the effective radiated power must be within statutory limits.
Signal level detectors often employ a diode envelope detector type of circuit. Such diode circuits are characterized by a limited dynamic range of input signals in which they can work, and they are highly sensitive to temperature variations. Many detector applications require a high degree of operating precision over a large signal range and over a wide temperature range necessitating complex and expensive measures to cope with the problems of temperature sensitivity and limited dynamic range of operation.
Schottky type diodes are often employed in such diode envelope detectors. These detector circuits are often divided according to two different types of operation. One is a low input signal, or square-law, detector in which the output voltage is a function of the square of the input voltage, or a function of the input power. Another type is the large signal, or linear-law, detector in which the output voltage is a function of the input voltage. The diode sensitivity to temperature variations is most severely evidenced in the square-law region of operation. It is known that diode detector circuits can be modified in order to alter either or both of the temperature sensitivity and the range of operation. In some cases, the circuit modifications must themselves be changed when the range of operation of the detector is to be altered. Consequently, envelope detectors which must operate under severe temperature conditions and over a large dynamic range of input signals, become quite complex and expensive.
For high power applications a detector having over 30 dB of range is increasingly often being required. The detector should be very stable with temperature, especially over the top 16 dB or so of range. Such a range from a simple low cost circuit is not easy to realize, as a diode response over this range is logarithmic.
A standard approach can give up to 28 dB range, with good temperature cancellation for the bottom part of the range, degrading as input power is increased. It is possible to force the current in a temperature sensing diode to equal that in the power detecting diode using feedback. This approach results in a complex circuit, which may not necessarily have the required range.
The required range could be achieved by using two separate operational amplifier circuits, one with high gain for the low part of the range, and one with low gain for the high part of the range. A separate circuit can then be used to switch between the two ranges, increasing system complexity. This would also require some form of hysteresis.
Another method would be to follow the diode detector with a xe2x80x98log amplifierxe2x80x99, which linearizes the response. Whilst this is a feasible solution it may have its complications. A super-matched pair of transistors would almost certainly be necessary to ensure temperature stability of the log amp circuit, increasing cost and complexity. Further, some form of temperature compensation for the detector diode would also be necessary.
U.S. Pat. No. 4,490,691 (Turner) provides a signal level detector employing diode circuits which are arranged to extend the continuous input signal range over which the detector can operate without user intervention to modify the detector circuits. The detector has both square-law and linear-law ranges of operation, and is provided with circuits for extending the linear-law range of its operation for effectively overlapping at least a part of a variable-law transition range which is between the linear-law and square-law ranges.
The present invention seeks to provide an improved power detector having an increased range. The present invention further seeks to provide an power detector having a range of over 30 dB. The present invention further seeks to provide a radio frequency power detector which is of a simple construction which lends itself to simple and cheap mass production techniques.
In accordance with a first aspect of the invention, there is provided a radio frequency power detector, which detector comprises a radio frequency coupler, a radio frequency to direct current voltage converter and an operational amplifier circuit to provide voltage scaling; wherein the operational amplifier circuit includes a plurality of amplifiers operable to scale the dc signals, and wherein the plurality of amplifiers are sequentially independently operable over particular ranges, whereby the full range of operation of the detector is determined by the discrete ranges of operation of the plurality of amplifiers.
Preferably the amplifiers are switched into operation by means of diodes which are brought into operation depending upon the gain and offset voltages for the respective amplifiers within the amplification circuitry. Whereby the diodes in the operational amplifier feed back loops automatically transfer from the one operating range to another dependent upon the input signal voltage. The switching operation of the amplifiers is similar to a wired OR connection used in digital electronics in that amplifiers U1 or U2 are switched.
Alternatively the amplifiers are switched into operation under microprocessor control or similar: when the output reaches a certain value then the circuit could be switched to a different amplifier. This switching system may result in an output curve having a hysteresis response in the transition region between the operating ranges of the two amplifiers.
Preferably, the radio frequency to direct current voltage converter is a Schottky diode detector. Preferably, the radio frequency to direct current voltage converter is a diode detector. Preferably, the diode detector has an additional diode to cancel the voltage drop occurring through the diode and to provide temperature tracking.
In accordance with a second aspect of the invention, there is provided a method of operating a radio frequency power detector, which detector comprises a radio frequency coupler, a radio frequency to direct current voltage converter and an operational amplifier circuit to provide voltage scaling; wherein the operational amplifier circuit includes a plurality of amplifiers operable to amplify the dc signals, and wherein the plurality of amplifiers are sequentially independently operable over particular ranges, whereby the full range of operation of the detector is determined by the discrete ranges of operation of the plurality of amplifiers, the method comprising the steps of coupling rf energy, converting the rf energy to direct current voltage and outputting a signal of voltage Vrf to an amplification circuit, and operating the amplifier appropriate for the particular level of voltage.
Preferably, the amplifiers are switched into operation by means of diodes which are brought into operation depending upon the gain and offset voltages for the respective amplifiers within the amplification circuitry. In the alternative, microprocessor control may be employed.
In accordance with a third aspect of the invention, there is provided a telecommunications cellular base station including a power detector arrangement comprising a radio frequency coupler, a radio frequency to direct current voltage converter and an operational amplifier circuit to provide voltage scaling; wherein the operational amplifier circuit includes a plurality of amplifiers operable to amplify the dc signals, and wherein the plurality of amplifiers are sequentially independently operable over particular ranges, whereby the full range of operation of the detector is determined by the discrete ranges of operation of the plurality of amplifiers.
In accordance with a fourth aspect of the invention, there is provided a method of operating a telecommunications cellular base station including a power detector arrangement; which detector comprises a radio frequency coupler, a radio frequency to direct current voltage converter and an operational amplifier circuit to provide voltage scaling; wherein the operational amplifier circuit includes a plurality of amplifiers operable to amplify the dc signals, and wherein the plurality of amplifiers are sequentially independently operable over particular ranges, whereby the full range of operation of the detector is determined by the discrete ranges of operation of the plurality of amplifiers, the method comprising the steps of coupling rf energy, converting the rf energy to direct current voltage and outputting a signal of voltage Vrf to an amplification circuit, and operating the amplifier appropriate for the particular level of voltage.
In accordance with a fifth aspect of the invention, there is provided a radio frequency coupler, a radio frequency to direct current voltage converter and an operational amplifier circuit to provide voltage scaling; wherein the operational amplifier circuit includes a plurality of amplifiers operable to amplify the dc signals, and wherein the plurality of amplifiers are sequentially independently operable over particular ranges, whereby the full range of operation of the detector is determined by the discrete ranges of operation of the plurality of amplifiers.
In accordance with a sixth aspect of the invention, there is provided a method of operating a telecommunications system including a power detector arrangement; which detector comprises a radio frequency coupler, a radio frequency to direct current voltage converter and an operational amplifier circuit to provide voltage scaling; wherein the operational amplifier circuit includes a plurality of amplifiers operable to amplify the dc signals, and wherein the plurality of amplifiers are sequentially independently operable over particular ranges, whereby the full range of operation of the detector is determined by the discrete ranges of operation of the plurality of amplifiers, the method comprising the steps of coupling rf energy, converting the rf energy to direct current voltage and outputting a signal of voltage Vrf to an amplification circuit, and operating the amplifier appropriate for the particular level of voltage.
In accordance with a seventh aspect of the invention, there is provided a amplifier circuit operable to .provide voltage scaling; wherein the amplifier circuit includes a plurality of amplifiers operable to scale dc signals, and wherein the plurality of amplifiers are sequentially independently operable over particular ranges, whereby the full range of operation of the circuit is determined by the discrete ranges of operation of the plurality of amplifiers.
In accordance with a eighth aspect of the invention, there is provided a method of operating an amplifier circuit operable to provide voltage scaling; wherein the amplifier circuit includes a plurality of amplifiers operable to scale the dc signals, and wherein the plurality of amplifiers are sequentially independently operable over particular ranges, whereby the full range of operation of the circuit is determined by the discrete ranges of operation of the plurality of amplifiers, the method comprising the steps of inputting a signal of dc voltage to the amplification circuit, and operating the amplifier appropriate for the particular level of voltage.
The present invention thus provides apparatus and methods of switching amplifier or attenuator blocks.